Vehicle restraint systems, also referred to as “seat belts”, are used to secure an occupant within a vehicle. A common vehicle restraint system includes a lap belt and a shoulder belt. Typically, the lap belt and the shoulder belt are connected together at one end and include a latch plate. The other end of the shoulder belt and lap belt is connected to the vehicle structure. A safety seatbelt buckle configured to receive the latch plate is also connected to the vehicle structure. When the buckle and the latch plate are connected (e.g., across an occupant's shoulder and waist), the vehicle restraint system may operate to restrain movement of the occupant, e.g., during breaking or a collision.
The buckle may identify whether a driver and/or an occupant wears the seatbelt. For this purpose, the buckle normally includes a mechanical switch such as a micro-switch that may be operated with a tongue of the belt. In one approach, the switch is actuated in response to the insertion or removal of the tongue, so that an indicator, e.g., on an instrument panel, is activated.
The buckle further may further include a self-diagnostic function, for example, in which a non-contact switch such as a hall sensor performs a self-diagnostic analysis of an electronic control unit (ECU). However, current art systems are limited to either a magnetic sensor circuit detection, where a magnet is actuated merely to detect lock and un-lock positions, or other kinds of sensing measurements such as an optical detector. Accuracy and reliability of these current art systems may be affected, however, by external mechanical vibration modes, application mechanical tolerances, and/or by external magnetic fields.